1. Field of the Invention
The present invention relates to an information recording/reproducing apparatus which has a protection function for protecting recorded information by executing a data converting process exceeding an error correction ability when the data is recorded.
2. Description of the Related Art
As an information recording/reproducing apparatus for recording and/or reproducing information on an information recording medium, a magnetic recording medium, such as a floppy disk or a magnetic card and an optical recording medium, such as an optical disk or an optical card are used. Although the optical recording medium cannot be rewritten, its large storage capacity permits an extensive application range, such as an optical disk used for recording image information and preserving documents and the optical card used for a bankbook, a portable map and a prepaid card for shopping.
Especially, the excellent portability of an optical card proposes the usage of recording personal information, such as personal health care information. Therefore, a measure for protecting the information peculiar to a person from eyes of others has been considered by encrypting of information.
For example, Japanese Patent Laid-Open No. 2-37527/1990 discloses an example in which a secret code as well as primary card characteristics including a reflectance of an optical card and an amplitude of a recording/reproducing signal are recorded when the optical card is produced or after examined. This prior art shown in FIG. 1 will be explained below.
A track part 92 is provided on an optical card 91. As primary characteristic data of an optical card, a preamble 94 containing GAP, VFO and SYNC, a track number 95, a card type A (format code) 96, a card type B (secret code) 97, a primary reflectance 98, a recording/reproducing signal amplitude 99 and a post amble 90 as GAP are recorded through a header 93 on the track part 92. The track part 92 has been previously formed in a stamper.
Also, the preamble 94 and the track number 95 may be simultaneously formed in the stamper with the track part 92. As the code used for secret-coding, for example, a rule for rearranging random numbers or numbers and letters can be used. When a pit pattern on an optical card can be easily detected with an optical microscope or the like and the secret code can be decoded, it is possible to choose which secret code for recording information on the optical card in the apparatus is used after several kinds of secret codes are put into a reading/writing apparatus.
There is a possibility that a pit pattern of an optical card on which the secret code obtained as the aforesaid is recorded is detected. Also, because a track or sector on which a secret code is recorded should be previously determined, a format of the optical card easily becomes different from the standard. Therefore, the usable range of the optical card is limited.
In the aforesaid example, generally, a secret number input by a user when the optical card recording/reproducing apparatus is used, and a secret number previously recorded on the optical card are read and compared. When they coincide, it is allowed to record/reproduce a data. When they do not coincide, it is prohibited to record/reproduce a data. Thus, an apparatus which includes the process of comparing such secret numbers with each other has an effect for protecting a data. However, an apparatus which does not include the process of comparing cannot attempt to protect a data, so that the data can be recorded/reproduced without constraints. Even if a data was encrypted, the feature that the data can be reproduced provides a chance for decryption and does not ensure protection of the recorded information.